Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive (HDD) to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model includes a storage disk or hard disk that spins at a designed rotational speed. An actuator arm is utilized to reach out over the disk. The arm carries a head assembly that has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The transducer is attached to a slider, such as an air-bearing slider, which is supported adjacent to the data surface of the disk by a cushion of air generated by the rotating disk. The transducer can also be attached to a contact-recording type slider. In either case, the slider is connected to the actuator arm by means of a suspension. The complete head assembly, e.g., the suspension and head, is called a head gimbal assembly (HGA).
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Over the years, the disk and the head have undergone great reductions in their size. Much of the refinement has been driven by consumer demand for smaller and more portable hard drives such as those used in personal digital assistants (PDAs), MP3 players, and the like. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that). Advances in magnetic recording are also primary reasons for the reduction in size.
This continual reduction in size has placed steadily increasing demands on the technology used in the HGA, particularly in terms of power consumption, shock performance, and disk real estate utilization. One recent advance in technology has been the development of the Femto slider, which is roughly one-third of the size and mass of the older Pico slider, which it replaces; over the past 23 years, slider size has been reduced by a factor of five, and mass by a factor of nearly 100.
One type of problem associated with hard disk drive technology is known as head crash, which is a phenomenon wherein a read/write head of a hard disk drive touches a rotating disk (or platter). Often when this occurs, the read/write head cannot return to its ramp and remains on top of the disk, commonly referred to as head on disk. It is pointed out that the damage to the hard disk drive caused by head crash can range from a loss of some data to complete inoperability of the hard disk drive. One of the causes of head crash is severe shock or vibration to a hard disk drive while one or more of its read/write heads are in operation. Some of the sources of severe shock or vibration can include dropping the hard disk drive onto a rigid surface, a hard external object or material colliding into the hard disk drive, and the like. Note that these sources of severe shock or vibration can accidentally occur to the hard disk drive even though care may be taken to handle and operate it.
One conventional technique used to protect a hard disk drive from head crash is to include a drop sensor within it. The idea behind this technique is that if the hard disk drive falls, the drop sensor is to detect the fall and then command the hard disk drive controller to suspend any current read/write operation and park the head safely away from the surface of the disk to prevent possible head disk contact. However, there are disadvantages associated with this technique. For example, in the event of an external object hitting the hard disk drive, the drop sensor technique is unable to detect the incoming object that will cause the severe shock or vibration. Another disadvantage is that the sensor technique only functions properly when the hard disk drive falls from a minimum height or higher. Otherwise the sensor technique is ineffective since it takes too long to complete its operation.